“Free Sugars” –what they are and why they are bad for your brain

There is quite a bit of research regarding dementia and Alzheimer’s diseases.  Many of the studies are pointing to High Fructose Corn Syrup (HFCS) as the main contributor to brain dysfunction.  HFCS is different from natural sugar found in fruits and vegetables.  It is considered a ‘free sugar’ because it is not packaged with the fiber that regular produce contains.

People who eat processed and refined foods consume more HFCS than people who opt for a more whole foods approach.  A study in June, 2022, found that rats that were fed HFCS developed negative changes in the brain.  These areas of the brain controlled memory, emotion, and other central nervous system functions.  The rats developed cognitive decline much like you would expect to see in an Alzheimer’s patient.

The American Journal of Clinical Nutrition reported in a study in March of 2023, that fructose may reduce metabolism in the brain.  The researchers have a hypothesis that increased fructose in the brain may increase the risk of brain dysfunction.  Keep in mind that the researchers make a distinction between HFCS and fructose that is found naturally in fruits and vegetables. 

Dr. Richard Johnson, professor at the University of Colorado School of  Medicine suspects that the ‘survival switch’ becomes stuck in the ‘on’ position when the brain receives too much ‘free sugar’.   The survival switch helps the body survive in times of famine.  When this switch is permanently on, people overeat high-fat sugary and salty foods, which leads to more sugar reaching the brain.

I have heard it said that Alzheimer’s Disease could really be called Type 3 Diabetes.  Just as the body cannot manage high blood sugar in Type 2, the brain cannot manage high sugar and function correctly.  This is an over simplification for sure, however, you can see some similarities.

Research shows that diabetic hyperglycemia causes the brain to misfire which leads to cognitive decline.  It is logical to assume that if we can control the way our bodies process sugar (have regular labs, diet change and lifestyle modifications) we can preserve our brain health.


A double-blind study at the University of California-Davis, showed that a fatty liver condition resulted in a decrease insulin sensitivity in people who consumed HFCS for just two weeks. 

The crucial point is this:   Fructose that comes from natural foods is quite different from HFCS which is added to process foods.  Fructose, glucose and sucrose that are separated from the fiber package nature gives us are what drives high sugar, both in the blood and in the brain.  The industrial food industry uses HFCS because it is cheap and it has a long shelf life.

Because people are aware that HFCS has a negative effect on blood sugar, they are shunning products that have HFCS in their ingredients.  However, many people do not know that the food industry has changed their packaging information and now HFCS is known by these 10 different names:

1. Maize syrup
2. Glucose syrup
3. Glucose-fructose syrup
4. Tapioca syrup
5. Fruit fructose
6. Crystalline fructose
7. HFCS (the same name, just the shortened version)
8. Isoglucose
9. Corn syrup
10. Dahlia syrup


The key take away is this:  If we want to preserve our cognitive function, then we must be selective of the type of foods we consume.  We must have awareness that the HFCS is not only sweet, but it is also addictive.  We must ration these treats not only for ourselves, but also for the children and elderly that are in our care.

Until next time,

Dr. Polly